1. Field of the Invention
The invention applies to the treatment of a flexible material such as metallic band, tube, wire or coil. It is concerned with an apparatus where the flexible material travels through a treatment volume in the shape of a helix so as to dip into a treating medium in the volume. This finds application in the treatment of surfaces of part-worked materials in metallurgy, such as chemical or electrolytic pickling, deposition, or so.
2. Description of the Prior Art
Examples of such apparatus are seen in above quoted U.S. patents wherein a flexible material such as a metallic strip or wire passes continuously through a tank or treatment volume following a helix-shaped path, this shape being imposed on said material by a set of driving and bending cylinders or rollers; the helical progression is made screw-wise as a result of the combined effects of one or more horizontal shafts carrying this helix and transmitting to same their rotary movement, and on the other hand, by a fixed horizontal comb of which teeth gear in the loops of said helix. The carrying shafts movement transmission is effected in a fixed ratio by the motor powering the input drive of material.
This makes for almost perfect functioning in normal working, although the treatment itself, which particularly has the effect of lessening or increasing the roughness of the material surface, causes a change, between inlet and outlet, of the frictional relationship between the material and the carrying shafts providing same its movement; this change is revealed by the development of a few loops of the helix relative to others, the loops where the material is the smoothest slipping the most and as a consequence getting longer than the others. As a result of this, the adjustment of the linear speed of the material inlet by reference to the size of sample loops, left for that purpose upstream of the treatment volume, is somewhat inaccurate because the control is not sufficiently representative of the behaviour of the helix inside the volume; in the same way the adjustment of the linear outlet speeds of the material by reference to the size of sample loops left for that purpose downstream of the treatment volume, is likewise imperfect. Mere amalgamation of these two adjustments is not enough to reach perfection. In addition these adjustments require the material to go helically past the inlet or outlet wall of the volume, as the case may be, which may imply an increase in pitch of the helix at that loop due to the fact that it must be wider than the wall which the material is passing over, which is harmful to the stability of the helix. But above all, experiment has shown that during starting up and slowing down of the material progression, the latter slips on the drive means at the inlet, the movement of which, transmitted to the carrying shafts, results in a slipping of the shafts on all the loops of the material; these slippings are noxious as they can mark the material locally. It should also be deemed that the loops of discrepant sizes also have discrepant contact times with the treating agent.